globstar in bash 4 follows directory symlinks

Globstar is a new feature is bash 4, allowing us to traverse a directory more easily.

Unfortunately, it follows directory symlinks and thus can easily cause problems.

(bleeding) desktop t # echo ${BASH_VERSINFO[@]}
4 0 17 2 release x86_64-pc-linux-gnu
(bleeding) desktop t # shopt -s globstar
(bleeding) desktop t # ls -l
total 0
lrwxrwxrwx 1 root root 1 2009-04-16 18:58 t -> .
(bleeding) desktop t # find
.
./t
(bleeding) desktop t # echo **
t t/t t/t/t t/t/t/t t/t/t/t/t t/t/t/t/t/t t/t/t/t/t/t/t t/t/t/t/t/t/t/t t/t/t/t/t/t/t/t/t t/t/t/t/t/t/t/t/t/t t/t/t/t/t/t/t/t/t/t/t t/t/t/t/t/t/t/t/t/t/t/t t/t/t/t/t/t/t/t/t/t/t/t/t t/t/t/t/t/t/t/t/t/t/t/t/t/t t/t/t/t/t/t/t/t/t/t/t/t/t/t/t t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t/t
(bleeding) desktop t #

Oh no…

If you unfortunately tried something like echo /proc/**/meminfo, it probably would make you wait for minutes before dying with “Insufficient memory.” (In /proc/fd there resides a root symlink.)

If you use GRUB to boot your Linux system, you are likely to find a symlink in /boot also named boot pointing to the directory itself. Yes, this is going to confuse bash, too. And there surely are many more cases.

So let’s continue writing find ... | xargs ...

Related posts:

1. How BASH Changes Terminal Window Title
2. Extended pattern matching in BASH
3. Dynamic library symlinks
4. Difference between dup(0) and open(“/dev/fd/0″,…);
5. BASH’s ‘read’ built-in supports ‘\0′ as delimiter

Tags: bash, shell